This work is directed toward developing a specific therapy, not now existent, for sickle cell disease and, as a means of achieving this end, toward the characterization of the physical chemistry of the gelation of sickle cell hemoglobin. Pathogenesis in sickle cell disease depends on the gelation of deoxyhemoglobuin S and on the intraerythrocytic abnormalities of rheology associated with this gelation. We have found that, contrary to previous assumptions, the 'gel' is solid-like, as the term 'gel' implies, and that its development and properties are highly dependent on the application of shear. The work under way and planned will extend these observations on the effects of shearing on gelation and the rheology of the highly thixotropic gel. Related work is directed toward characterization of the thermodynamics of gelation and the separate equilibria of aggregation and phase separation which occur. Most generally, this system is related to other polymerizing systems such as tubulin, actin, tobacco mosaic virus and flagellin in exhibiting helical aggregation and having the potential for phase separation. It may therefore be prototypic, or at least in some degree representative, or an important class of biopolymers.